Do the neocortical and tectal commissures of the mammalian brain facilitate the processing of information? We are trying to find out if bilateral brain function is more efficient when these structures are intact than when they have been sectioned. We have trained cats bilaterally on a stimulus detection task requiring a high level of performance in response to target stimuli in visual displays which vary over a wide range of complexity and which we change from trial to trial. The task places a premium on the subject's ability to attend; on his accuracy and perceptual speed (stimulus duration thresholds are measured); and his ability to respond appropriately to differences and similarities among stimuli (i.e., to discriminate and generalize). Also, the subjects' response to a "natural" target is tested (e.g., their attentive orientation to a visible but unreachable prey (a live mouse) is measured). Subjects are trained and tested rigorously before and after section of neocortical commissures (corpus callosum, anterior, hippocampal and habenular commissures) or pretectal and tectal commissures (posterior commissure superior and inferior colliculi commissures). Upon completion of the above series, we will study the loss of capacity which occurs when complex task information is confined to one side of the brain and why the loss is always greater for one than for the other brain half.